1. Field of the Invention
The invention relates to a locking device having particular utility for use with a fluid pressure actuator. The device can be released from its locked position by the occurrence of an elevated temperature immediate the device.
2. Description of the Prior Art
Temperature released locking mechanisms have heretofore been provided for fluid pressure actuators for valves. Such mechanisms have generally incorporated a mass of fusible material to hold the locking elements of the device in a locked position until the occurrence of an undesirably high temperature immediate the device. Because a relatively large mass of fusible material is employed in such devices, the actuator has to be exposed to the elevated temperature for a substantial time period in order for the mass of the fusible material to be sufficiently heated to cause it to melt and permit the locking device to move to an unlocked position. Moreover, such devices cannot be readily reconstructed in the field after they have once functioned in response to an elevated temperature because of the difficulty of melting and re-applying fusible material.
In U.S. Pat. No. 4,263,839, issued Apr. 28, 1981 and entitled "Heat Sensitive Locking Device", and assigned to the assignee of the instant application, there is disclosed and claimed a heat sensitive locking device wherein a plurality of locking segments are pivotally mounted within a collar for radial movement into locking engagement with a shaftlike element which, in turn, is rigidly secured to the shaft of the fluid pressure actuator. The locking segments are retained in their radially compressed, locked position by the wrapping of a spring wire around the periphery of the locking segments and the securement of the ends of the spring wire by a relatively small mass locking clip of fusible material. Thus, upon the occurrence of an elevated temperature sufficient to cause the small eutectic portion of the locking clip to melt, the spring wire is released and the locking segments are freed to move radially outwardly and permit the actuator to return to the axial position to which it is spring-biased.
While this structure has been effective insofar as providing a reliable and reusable temperature sensitive locking device for an actuator, it is relatively expensive to manufacture due to the large number of components involved in the structure of such device. It also requires a comparatively long time to assemble to an actuator.
There is, therefore, a need for a heat sensitive lock for a fluid pressure actuator utilizing a mechanism that includes a minimum number of component parts that may be readily and quickly assembled to the actuator.